1. Field of the Invention
This invention relates to spacecraft and the employment of thermal radiators in the form of heat conductive panels for the rejection of waste heat, and more particularly to a control system for thermally coupling and decoupling thermal radiator tubes to and from the radiator panel.
2. Description of the Prior Art
Heat transfer is difficult in spacecraft due to the absence of gravity and the presence of low vacuum conditions. Heat transfer has been effected both by the forced flow of coolant media either in liquid or gaseous form through suitable heat conductive tubes and by the employment of heat pipes. Heat pipes comprise an envelope or tube carrying internally on the envelope or tube surface or by a separate member, a capillary flow path and being provided with a mass of vaporizable working fluid such that by heating one end of the tube or envelope, working fluid in liquid form is vaporized and travels as vapor through the internal space of the tube to its other end, where heat is rejected during condensation of the working fluid, and the condensed working fluid travels back again to the end of the tube which is subjected to heat input by capillary action defining a loop process causing heat transfer from one end to the other.
In order to dissipate waste heat within manned and unmanned spacecraft, earth satellites and the like, conventionally the heat has been transmitted to planar heat conductive members constituting planar heat radiators which radiate the waste heat away from the spacecraft body. Conventionally, coolant tubes or heat pipes are mounted in heat transfer fashion to the surface of the planar heat radiator panel. Attempts have been made to control the extent of heat rejection by controlling the flow of heat from the heat pipes or radiator tubes to the radiator panels. Prior practices include by-pass control, regenerative heat exchange control, and stagnation control. By-pass control requires auxiliary heat to be added during low load conditions which in turn requires an auxiliary source of heat to that resulting during heavy load and of course mandating the necessity for effective rejection of the waste heat. Regenerative control functions adequately, but the weight of the regenerator required for wide heat load ranges establishes practical limits on this method of the rate of waste heat rejection. Stagnation control is also quite effective and was used on the Apollo project with a 2.5 to 1 load range. However, the stagnation control is subject to possible tube splitting which occurs during freezing of the coolant, and further, in changing from low to high heat transfer load, excessive time is required (up to two hours in an examplary system).
It is, therefore, a primary object of this invention to provide a waste heat rejection control system for wide heat load space vehicle radiators which does not require freezing of the radiator tubes and has a rapid response from minimum to maximum heat transfer loads.
There has been developed a movable joint structure for an assembly subjected to cryogenic temperatures within a vacuum environment and incorporating paired heat pipes which are mounted to respective interengaging relatively movable heat conductive heat pipe support members which define a gap between the support members. U.S. patent application Ser. No. 700,366 filed June 28, 1976, entitled "Gas Filled Swivel Joint for Cryogenic Heat Pipes", now U.S. Pat. No. 4069864 and assigned to the common assignee, employs ball and socket conductive support members permitting rotation of one heat pipe relative to the other about orthogonal axes with a pressurized gas interposed between the spherical opposed surfaces of the ball and socket support members to achieve a low impedance heat path across the gap between the ball and socket support members.
It is, therefore, a further object of the present invention to employ a pneumatic control technique to achieve the thermal coupling and decoupling of the radiator tubes fixed to the radiator panel, to coaxial, internal, longitudinally extending coolant tubes or heat pipes, and by modulation of the gas pressure achieve a variable thermal impedance path between the concentric tube array formed thereby.